1. Field of the Invention
The present invention relates to an explosion-preventing suspension insulator which can prevent explosive breakage of an insulator body due to flashover inside the cap. The insulator has substantially the same mechanical strength as that of ordinary suspension insulators.
2. Related Art Statement
When an ordinary suspension insulator is damaged due to a mechanical external force such as that which occurs from a bullet or an electrical external force such as from lightning attack, and a crack extends to a head portion of the insulator body, the insulator will be able to withstand a mechanical working load. However, if an abnormal voltage is applied in this state, it may be that an internal flashover takes place along the surface of the crack inside the cap, and the head portion of the insulator body will break due to an explosively increased internal pressure caused by the internal flashover, which may cause a serious accident in that the insulator string will break. As disclosed in Japanese Patent Publication No. 3,589/70, NGK Insulators, Ltd. have invented a suspension insulator in which the internal flashover is prevented, even upon receiving an abnormal voltage, by forming an insulating layer on the internal surface of a metal cap and the outer surface of a metal pin. However, such an explosion-preventing type suspension insulator is unsatisfactory in reliability because the internal flashover-preventing rate is about 85%. Further, since this suspension insulator has a defect that the mechanical performance cannot be stably maintained, it has not been widely practically used.